The present invention relates to a lift arm device and an industrial vehicle having the lift arm device.
Japanese Patent No. 3133793 indicates that, in a skid steer loader having a loader boom which is mounted at a single pivotal axis to the frame of the skid steer loader, the outer front end of the loader boom travels along an arcuate path when the boom is raised or lowered, with the result that the forward reach of a working implement such as bucket provided at the front end of the loader boom tends to be shortened.
In order to solve such problem, the following construction is disclosed in Japanese Patent No. 3133793. A main lift arm section to which a bucket is attached is connected to the main frame of the loader through two links (or a rear lift arm link and a rigid link) and an actuator. Each of the two links and the actuator is connected at one end thereof to the main lift arm section through a pin and at the other end thereof to the main frame of the loader through a pin.
According to the Patent, the main lift arm can have a longer reach in the upper region of its path of movement, so that loading and unloading operation, such as unloading into a truck and making a higher pile, can be performed easily.
U.S. Pat. No. 6,705,826 discloses a lift truck which includes a boom whose proximal end is pivotally connected not directly to a mobile frame but to a support which can be moved horizontally in the longitudinal direction of the frame. When the boom is raised by one cylinder, the support is displaced by another cylinder. Thus, the front end of the boom travels in an almost vertical path, thereby increasing the load capacity. Each of the two cylinders is pivotally connected at one end thereof to the frame and at the other end thereof to the boom or the support.
In the skid steer loader disclosed in the above-cited Japanese Patent No. 3133793, a longer reach of the main lift arm section is obtained in the raised position of the lift arm. However, the skid steer loader has no degree of freedom for the path of movement of the lift arm. In order to change the path of movement that has been set once, the lift arm and its associated parts need to be modified significantly. Therefore, it has been hard for the conventional skid steer loader to be used under various conditions or for various specific purposes.
In the lift truck disclosed in U.S. Pat. No. 6,705,826, the operation of the cylinder for displacing the support is determined by the control as shown in FIGS. 6 through 10 of the patent in accordance with the raised amount of the boom by the other cylinder. Thus, it is hard for the above lift truck to provide the degree of freedom for the path of movement of the lift arm. Furthermore, the lift truck having the support which is moved horizontally in the longitudinal direction of the frame needs to increase the displaced amount of the support for obtaining a longer reach of the boom in an upper raised position. Thus, a larger space is needed for movement of guide means for the support (or horizontal rod 18) and the support, which causes its raising and lowering device and hence the industrial vehicle to be made larger in size.